The present invention relates to a fastening element for joining two structural members such as two pieces of girder of which one has a slot with lips at the sides thereof, the fastening element being so designed that the two members may be separated again when desired. More specially the invention relates to such an expanding fastening element made up of two legs that are hinged together and may be opened out by way of a fixing screw into a locking or gripping position with hook-like heads of the legs hooked onto the lips. Before tightening the screw the fastening element is positioned as desired in a hole in one girder by a side guide sleeve or plug locking into the second member and springingly pushed outwards from the fastening element by a spring within it.
In the past a number of different forms of expanding fastening elements have been designed for making connections between structural members, as for example between horizontal girders or wall elements and upright girders so that the connections made may be undone later when desired. One example is to be seen in Norwegian Pat. No. 96,260 using a cotter-like connection part, whose front end is slotted, having a fixing screw placed on one side of the slot for opening up the slotted part of the fastening element and moving hook-like end parts against the sides of holes in upright structural elements. As a further example, German Auslegeschrift specification No. 1,054,320 makes use of a support bracket, that is placed in a support rail and has hooked heads which are opened out and forced away from each other by a fixing screw so that they become locked onto lips at the sides of an opening in the support rail. German Auslegeschrift specification No. 1,302,838 relates to a system of frame-making elements, which are joined together by using two flat connection arms on one such frame part, which are plugged into a frame girder so that hooked ends of the arms may be forced outwards by spring force and then locked in position by an eccentric.
To take a further example of the prior art, German Gebrauchsmuster patent (utility model) No. 7,501,856 relates to an expanding plug made up of two hinged-together legs with hooked, outwardly bent ends, that may be fixed in position with a gripping effect and then locked by an eccentric. This expansion fastening element has a spring-like u-part for pulling back the legs out of the gripping position, at the back end of the fastening element. The two legs are joined together by a hinge at a back end.
German Offenlegungschrift specification No. 2,906,281 relates to a coupling element for rails or girders with lengthways slots using freely turning legs or gripping jaws which are forced outwards by a compression spring and are opened up by way of a fixing screw acting on the other of the two legs by way of a further spring. One form of the coupling element has a guide sleeve as well that is acted upon by a spring pushing it outwards so that it will be snapped into an opening in the wall of a hole into which the coupling element is slipped. The purpose said to be effected by this prior art design of coupling is that even before the fixing system is operated a friction connection may be produced between the hook heads of the coupling element and the edges of the slot or groove in the girder element so that the coupling element is simpler to put in place and is more simply handled.